Electroless copper plating has many important commercial applications. One of these is the manufacture of printed circuits by an additive process. Electroless copper plating is also used for providing plastics with decorative metallic coatings.
The most widely used electroless copper plating baths all include formaldehyde as the agent which causes the copper to be reduced from solution. Although these baths are generally satisfactory, it would be desirable to have baths that plate at a faster rate so that more product could be plated without increasing the most of equipment. At the same time, however, the increased plating rate must not be at the cost of greatly decreased bath stability or the addition of expensive ingredients.
The present invention resides in the discovery that if sodium hypophosite is added to conventional formaldehyde-containing electroless copper plating baths in controlled amounts, a significant increase in plating rate can be obtained with very little increase in cost. Although sodium hypophosphite is, itself, a reducing agent in electroless nickel, cobalt, palladium and silver plating baths, it is not a satisfactory reducing agent (i.e., will not reduce Cu.sup.+.sup.+ .fwdarw. Cu.degree.) when used alone in alkaline electroless copper plating baths. In the baths of the present invention, the sodium hypophosphite is not used up in the plating reaction. Instead, it appears to act as a catalyst.